Field
Apparatuses consistent with exemplary embodiments relate to photonic crystal type light modulators and 3D image acquisition apparatuses employing the same.
Description of the Related Art
An optical shutter having a function of transmitting or blocking an optical image according to a control signal is widely used in photographing apparatuses such as cameras and in displaying apparatuses such as liquid crystal display (LCD) apparatuses.
With respect to its operating technique, an optical shutter may be a mechanical shutter, as used in cameras, a liquid crystal (LC) shutter, as used in LCDs, a digital micro-mirror device (DMD), as used in projection displays, a spatial light modulator (SLM) based on a micro electromechanical system (MEMS) such as grating light valves (GLVs), or an intensifier- or a semiconductor-based optical shutter, as used in laser radar (LADAR) and 3D cameras.
With respect to the driving principle and shutter speed of its optical shutter, a mechanical shutter is driven by an electro-magnetic motor and generally has shutter time of 1 ms; an LC shutter is driven by a rotational motion of LC which reacts to an electric field and has shutter time of a few ms; an SLM based on MEMS technology drives a fine structure using an electrostatic force and has an operational time of several tens of μs; an image intensifier and semiconductor-based optical shutters are driven by a photoelectric transformation of a semiconductor and have a shutter time of several tens of ns.
Currently, 3D cameras or LADAR technology that record distance information of an object measure a distance between a photographing apparatus and an object being photographed by using a time-of-flight method. According to a shuttered light pulse (SLP) method, which is a type of time-of-flight method, light having a specific wavelength (for example: near infrared (NIR) light with a wavelength of 850 nm) is projected onto an object to be photographed and a light image having the same wavelength reflected from the object to be photographed is shuttered. Then, an image is acquired through an imaging device and distance information is acquired through a series of processes. In order to determine a moving time of the reflected light according to distance, a rapid shutter time of 1 ns is required. Therefore, a high-speed optical image shutter is needed. Accordingly, an image intensifier or a semiconductor based optical shutter is used. However, an image intensifier is high-priced equipment that requires a high voltage and vacuum packaging, and semiconductor based optical shutters are manufactured on GaAs substrates using a semiconductor manufacturing process and have complex structures as compared with a general photo-diode or an LED. Thus, it is difficult to commercialize a semiconductor based optical shutter due to its price and the difficulty of manufacturing it.